You can use the error function. It accepts a string that is displayed
when the error is evaluated:
> GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help
> Loading package ghc-prim ... linking ... done.
> Loading package integer ... linking ... done.
> Loading package base ... linking ... done.
> Prelude> error "hi!"
> *** Exception: hi!
HTH,
Martijn.
Andrew U. Frank wrote:
> is there a way to have different kinds of undefined? such that i get a message
> which one was hit. something like writing in the code 'unefined 'my error 123'
> which prints 'undefined - my error 123' when it is accidentally hit.